Research On Optimization Of Direct Torque Control Strategy Of Speed Sensorless Induction Motor

Direct torque control is a new strategy of AC speed regulation after field-oriented control.Compared with the complex coordinate transformation of field-oriented control strategy,direct torque control strategy has simple structure,novel idea and strong robustness,so it is widely used in the control of induction motor,permanent magnet synchronous motor and other motors.Speed feedback is necessary in high-performance AC speed regulation system.Usually,high-precision photoelectric encoder is used to observe the motor speed in real-time.However,the use of photoelectric encoder increases the hardware cost and reduces the reliability.The proposal of speed-sensorless method effectively solves this problem.In this paper,the working principle and control method of speed-sensorless induction motor direct torque control system are studied.In this paper,the basic structure and working principle of induction motor are studied,and the mathematical model of the induction motor in two-phase static coordinate system is established.The traditional direct torque control is analyzed.According to the motor torque and flux ripple,the voltage vector selection in the process of sector switching is analyzed in detail.The effects of traditional 6-sector and 12-sector on torque and flux pulsation suppression are compared and analyzed.The basic principles,parameter selection and compensation scheme of double low-pass filter(DLPF)are analyzed in detail,compare and analyze its improvement relative to low-pass filter,and apply DLPF to the model reference adaptive system(Model Reference Adaptive System,MRAS)constitutes the DLPF-MRAS direct torque control system in the reference model.The DLPF-MRAS direct torque control system is simulated and compared with the traditional direct torque control system,and the waveform optimization effect of the former on key parameters such as torque and three-phase current is analyzed.The new direct torque control system in this paper combines 12-sector subdivision and DLPF-MRAS,the simulation models of the traditional direct torque control system and the new direct torque control system are built respectively.The speed waveforms of the new direct torque control system under the dynamic and static conditions are analyzed.At the same time,the torque,three-phase current and stator flux linkage waveforms of the two systems are compared and analyzed.The experimental hardware platform is built to verify the new direct torque control system.The simulation and experimental results prove the correctness of the theory.